1. Field of the Invention
The present invention relates to a damping device for a rotor supported by an arrangement of magnetic bearings including at least one radial bearing formed of a stator magnet and a rotor magnet.
2. Description of the Prior Art
Different versions of electronically controlled or mechanically supported magnet bearings for contactless support of rapidly rotating rotors are disclosed in literature. A common feature for all of them is an occurrence of axial and radial oscillations which mark resonance positions of the rotor, in particular at continuous rotation. This can lead to critical situations when magnetic bearings are used for rotors, with which very narrow tolerances should be used, e.g., for rotors of turbomolecular pumps. Such critical situations can result in running of rotors into stators and to the destruction of the entire apparatus. Therefore, it is important to provide these bearings with appropriate damping elements to insure a reliable and quiet operation of the rotor.
There are different methods for damping of magnetically supported rotors. Here, in particular, methods used for damping of radial magnetic elements are considered. At that, damping with eddy currents is of a small interest because they have poor damping characteristics. However, damping devices, in which an intermediate member is used, proved themselves. German Patent No. 2,658,925 and a book by Pollermann "Constructional Elements of Physical Technology" (Bauelemente der physikalischen Technik), Springer-Verlag, 1955, pp. 97-98, disclose mechanical damping elements which act on a rotor via an intermediate member. However, the intermediate members used there are not fixed axially. For rotors, which have only minimal axial tolerances, these damping elements are not suitable. Other solutions require the use of intermediate members having a relatively large mass which negatively influences the damping characteristics of respective devices. Also known are mechanical damping devices in which fluid-filled constructional elements are used. Poor damping characteristics and an unreliable operation limit the possibilities of use of such devices. Complicated constructions, e.g., ones disclosed in German Publication DE-05 32 39328 or constructions which require an extensive centering of the intermediate member, do not constitute an advantageous solution.
Accordingly, an object of the present invention is to provide a damping device for a magnetically supported rotor without the above-listed drawbacks.
Another object of the present invention is to provide a mechanical damping device with an intermediate member which is axially fixed but is radially displaceable.
A further object of the present invention is to provide a damping device with an intermediate member which has a simple structure, in which the geometrical expansion of elements is kept within certain limits, and in which the centering is insured with simple means.
A still further object of the present invention is a damping device with an intermediate member and having a minimum of additional constructional elements.